scsi: mpi3mr: A performance fix

scsi: mpi3mr: A performance fix

Commit 0c52310f2600 ("hrtimer: Ignore slack time for RT tasks in
schedule_hrtimeout_range()") effectivelly shortens a sleep in a polling
function in the driver.  That is causing a performance regression as the
new value of just 2us is too low, in certain tests the perf drop is ~30%.
Fix this by adjusting the sleep to 20us (close to the previous value).

Reported-by: Jan Jurca <jjurca@redhat.com>
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Link: https://lore.kernel.org/r/20240903144729.37218-1-thenzl@redhat.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>